Bosch Cost-Effective Induction Loop Amplifier


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The PLN-1LA10 Loop Amplifier is a cost-effective amplifier designed to drive a wire loop installed in the floor or ceiling, covering an area of up to 600 m2 per amplifier. This solution enables hearing-aid users in the area enclosed by the wire loop to hear all announcements, or music. Hearing-aid users can set their devices to the T-mode setting to receive the signal coming from the loop. They receive announcements in excellent audio-quality, without the background noise or reverberations that normally impair intelligibility for people with hearing disabilities.

The loop amplifier can be connected to a mixing amplifier’s line level output, or it can accept up to two microphone/line signals directly. A 100 V priority input is available for uplink to a Plena Voice Alarm System. This input can be monitored for the presence of a pilot-tone. The built-in supervision monitors all key functions of the loop amplifier, and the fault state is available on a fail-safe relay. This makes it possible to use the loop amplifier in an emergency sound system, and to include the induction loop in the supervised transmission paths. 

For added ease, the loop amplifier is equipped with a limiter that keeps the output field strength below the prescribed 100 mA/m. This circuitry can also be set to an automatic gain control (AGC) that amplifies weak signals for enhanced intelligibility, while attenuating loud signals. This ensures that all information is presented at a comfortable listening level. The unit has tone controls and a metal loss compensation circuit to adjust the sound to the program material and the environment. The controls have locks to prevent unwanted access after they have been adjusted. The loop amplifier is stackable (master/slave configuration) to cover very large areas, and supports low spillover schemes. Its unique quadrate configuration provides uniform field strengths even over multiple loops.

Controls and Indicators


  • LED power meter
  • Current meter
  • Four LEDS for fault, AGC, loop integrity
  • Headphones socket
  • Two tone controls
  • Three input volume controls(master and two channels)
  • On/Off switch


  • Metal loss compensation control
  • Supervision switch
  • Voltage selector
  • Frequency range switch

Technical Specifications

Mains power supply
Voltage 230/115 VAC, 10%, 50/60 Hz
Inrush current 7 A at 230 VAC / 14A at 115 VAC
Max power consumption 500 VA
Output current 10 A
Frequency Response 50 Hz to 10 kHz (+1/-3 dB at -10 dB ref. rated output)  
Distortion <1% at rated output power, 1kHz
Bass Control -8/+8 dB at 100 Hz
Treble Control -8/+8 dB at 10 kHz
Mic/Line Input 2x
Connector 3-Pin XLR, balanced mic/line level (switchable)
Sensitivity 1mV/1V (mic/line)
Impedance >1k ohm
Dynamic Range 100 dB
S/N (flat at max volume) 75 dB
Headroom 25 dB
Phantom power supply 16V (switchable)
VOX functionality Input 1 (switchable) mutes input 2
VOX sensitivity -10dB ref nominal input
Priority input 
Connector Screw
Sensitivity 100V, transformer balanced
Impedance >100 kohm
S/N (flat at max volume)     63 dB
Headroom 25 dB 
Pilot tone detection  -20 dB, ref 100 V (10 V) 
Pilot tone threshold -26 dB, ref 100 V (5 V)
Master input* 1 x
Connector  1/4" TS jack 
Line output
Connector  3-pin XLR, balanced 
Nominal level 1 V 
Impedance  200 ohm 
Loop output 
Connector Screw 
Slave output (for master input of other PLN-1LA10) 
Connector  1/4”TS jack 0 to 90
Fault Relay
Connector Screw
Contacts  100 V, 2 A (voltage free, SPDT)


Dimensions (H x W x D)     94 x 430 x 320 mm

(19" wide, 2U high)

Weight Approx. 11.6 kg 
Mounting Stand-alone, 19" rack 
Color  Charcoal 


Operating temperature -10 C to +55 C (14 F to +131 F) 
Storage and transport temperature      40 C to +70 C (-40 F to +158 F)
Relative humidity  <95% 
Acoustic noise level of fan  <35 dB SPL at 1m, temperature controlled